Kinetic Simulations of H2 Production from H2S Pyrolysis in Sulfur Recovery Units Using a Detailed Reaction Mechanism

Acid gas (H2S and CO2) is produced in large volumes worldwide from the desulfurization of hydrocarbon fuels and is utilized in sulfur recovery units (SRUs) to produce sulfur. However, the hydrogen content of acid gas is wasted as low-grade steam, which highlights the need for the efficient utilization of this resource. The production of H2 from acid gas is desired, as it is an inexpensive feedstock. In this work, a kinetic study is conducted on H2 production from acid gas in an industrial SRU to utilize its built-in inertia, while saving on the capital cost and enhancing the processing capacity of the SRU. The thermal energy generated during the combustion of acid gas in the reaction furnace (RF) is used for acid gas pyrolysis in the waste heat boiler (WHB) of the SRU. While this technique has been investigated previously, its realization at the industrial scale is hindered by low H2 yield. This paper presents suitable means of enhancing H2 production via operational modifications in RF and WHB. A detailed reaction mechanism, developed for acid gas combustion and pyrolysis and validated using experimental data from industrial furnaces and reactors, is used for the kinetic simulations of the SRU thermal unit. The results show that RF operational changes such as the extent of H2S oxidation and feed preheating can increase H2 yield from 3% to 38% in the WHB without changing the composition of the acid gas stream. This significant improvement in H2 yield can help in realizing its production from acid gas in SRUs.